UPDATE: More homes could be evacuated as firefighters continue to battle a massive blaze at a Coolaroo recycling plant.

MFB crews expect it will take up to three days to control the fire, which started at the Maffra Street plant on Thursday morning.

Emergency Services Minister James Merlino told reporters this morning that it was “highly likely” there would be further recommendations to evacuate.

“This will be the decision of the chief health officer, the EPA, department of health and human services,” he said.

Mr Merlino said the fire was the size of a sports field and as high as a factory.

He said fire crews had faced very complex, chanllenging, dirty and dangerous work.

MFB acting deputy chief fire officer Ken Brown said meetings had been held with residents and local businesses to keep them updated.

Another community meeting will be held at the Broadmeadows Aquatic and Leisure Centre at 6.30pm.

Mr Brown said the changing weather made it difficult for firefighters to put a “really good” timeline on the fire.

“The size of the site and the ability to move material around is also making it complex,” he said.

Police and SES crews door-knocked about 115 households in the Dallas area last night after an evacuation order was issued about 8.10pm.

The Environment Protection Authority has rated the area’s air quality as “very poor”.

The areas evacuated include Barry Road between Dallas Drive and Doy Street, Washington Street between King Street and Doy Street, Edmund Street between King Street and Doy Street, Doy Street between Barry Road and Edmund Street and Dallas Drive to Sale Court, including Sale Court.

Twenty-two people were evacuated from their homes, while 41 attended a relief centre set up at the Broadmeadows Aquatic and Leisure Centre.

Four people, including a four-year-old girl, have been taken to hospital in stable conditions.

Residents in Broadmeadows, Campbellfield, Dallas, Fawkner, Glenroy, Jacana and Westmeadows have been put on a watch-and-act warning as acrid smoke continued to blanket Melbourne’s northern suburbs. People in those suburbs have been told to shelter indoors, close all exterior doors, windows and vents, and turn off heating and cooling systems.

The fire at the SKM recycling plant on Maffra Street started just before 9am yesterday.

Firefighters have contained the blaze within the perimeter of the plant, but it is not yet under control. It is not known when the fire will be extinguished.

About 160 firefighters remain at the scene.

The fire is the third at the recycling plant in the past four months, following incidents in February and June.

Hume mayor Drew Jessop praised the efforts of emergency service crews and urged residents to remain up-to-date about the situation.

“We remind residents to follow the advice of emergency services,” he said. “Anyone with pre-existing respiratory condition needs to continue to monitor their condition closely.

“We appreciate that it has been a difficult day for our community and its surrounds, and we can only hope the situation is resolved as soon as possible.”